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The Origin of the Ionised Universe

Shortly after the Big Bang, a veil was lifted from the cosmos, transforming the cold and dark Universe into a hot and luminous birthplace for stars and galaxies

During this period, called the Epoch of Reionisation, massive amounts of energy transformed the hydrogen gas in the Universe from a neutral state into an ionised state. Now, more than 99% of the atoms in Universe are ionised, but how the Universe reached this state is unknown. When did the veil rise, and how long did it take?

 

IMAGE: ROBIN DIENEL (COURTESY OF THE CARNEGIE INSTITUTE FOR SCIENCE)

What first created such massive amounts of energy? What did the first generation of stars and galaxies look like, when did they form, and how did they evolve? Can we see the fossil records of those first stars today? ASTRO 3D is uniquely poised to measure and characterise the beginning and end of reionisation, the sources of reionisation, and the conditions at the Epoch of Reionisation.

 

The world’s largest ground and space telescopes, and the world’s most powerful supercomputers have now laid the foundation required for this research. We now know that the source of reionisation is likely to be light from the first stars. Theoretical models on the world’s supercomputers can now predict how galaxies formed and evolved from shortly after the Big Bang to the present day. In ASTRO-3D, by combining Australia’s theoretical and multi-wavelength observational expertise with innovative instruments and telescopes, we are lifting the veil on the Epoch of Reionisation, demonstrating how this landmark event evolved into the Universe that surrounds us today. We are:

  • Employing the Murchison Widefield Array (MWA) in WA to detect the structure created by the first ionizing sources in the Universe using the power spectrum of neutral Hydrogen.
  • Measuring when the reionisation of the Universe occurred, and how long this important process lasted.
  • Investigating the conditions under which these first stars in the Universe were born with the ESO 8-10m telescopes
  • Using the ESO 8-10m telescopes to track the ionizing radiation in galaxies over the past 12 billion years using luminous emission-lines in galaxy spectra created by atoms in gas clouds that are ionised and excited by young, hot stars, massive shock fronts from galactic-scale winds, or supermassive black holes in the centres of galaxies and will bridge the gap between first galaxies and the local Universe.

These observational studies will set stringent boundary conditions on our new state-of-the-art Genesis theoretical simulations that span the Epoch of Reionisation to the present day.

 

IMAGE: CALTECH/S.G. DJORGOVSKI ET AL